Microwave Challenges to the Thermoregulatory System,

Abstract

Approved for public release; distribution is unlimited. 10 Thermoregulation Prepared for USAF SCHOOL OF AEROSPACE MEDICINE S9. ABSTRACT (Continue on reverse if necessary and identify by block number)Three experiments were conducted to measure the upper tolerance limit for maintaining thermal balance in squirrel monkeys during exposure to 2450-MHz radiofrequency radiation (RFR). During microwave exposure at high intensity, thermoregulatory behavior, metabolic, vasomotor, and sudomotor responses were mobilized in normal fashion, but the capacity to lose heat through sweating was found to be the limiting factor in microwave tolerance. The major conclusion drawn from these studies is that the thermoregulatory system deals with energy absorbed from microwave fields in exactly the same way as energy produced in the body by normal metabolic processes or absorbed during exposure to conventional radiant or convective heat sources. i UNCLASSIFIED SUMMARYExposure to low-intensity radiofrequency (RF) fields influences the normal responses, both autonomic and behavioral, that regulate the body temperature.In the past, we have used the squirrel monkey as an animal model to determine the minimal incident energy (in mW/cm 2 ) derived from 2450-M z continuous wave (CW) microwaves that is necessary to lower an elevated metabolic heat production in the cold, alter peripheral vasomotor tone in thermoneutral environments, initiate sweating in the heat, and alter thermoregulatory behavior. In all cases, the threshold power density is remarkably similar (4-8 mW/cm 2 ), a finding that suggests a common thermal basis for the response changes. The whole-body specific absorption rate (SAR) at threshold is equivalent to 15-20Z of the resting metabolic heat production (M_) of the subject animal. Above the threshold level, at least to SARa equivalent to two-thirds resting !!, the mobilized thermoregulatory responses ensure that the body temperature is regulated with precision at the normal level and the magnitude of the response change is usually a linear function of field strength. The three experimentsreported here sought to determine the upper limit of these functions, that is, the ceiling intensity that can be effectively dealt with by normal thermoregulatory processes.Experiment 1 measured changes in ambient temperature (T a ) selected by highly trained squirrel monkeys during both transient (10 min) and steady-state (90 min) whole-body microwave exposures at high power densities (up to 70 mw/cmW 2 ). During transient exposures, all power densities tested were countered by behavioral selection of a cooler environment so that the body temperatures were regulated at close to the normal level; 45 mW/cm 2 was similarly well tolerated by all animals in the steady-state. Thus, no upper tolerance limit was found for behavioral thermoregulation.Experiment 2 assessed the potential for disruption of autonomic thermoregulation by an altered metabolic state (induced by injections of isoproterenol) in squirrel monkeys exposed to microwaves in a ther...

Thermoregulatory responses to RF energy absorption

“…During acute far field RF exposure of the whole body in cold T a , the elevated M of nonhuman primates is reduced by an amount proportional to the PD or the SAR [Adair and Adams, 1982;Adair, 1985Adair, , 1987aLotz, 1985;Saxton, 1987, 1988;. As a result of this M adjustment, T co is usually regulated within the normal limits for the species.…”

Behavioral and cognitive effects of microwave exposure

“…During 2.5 h RF exposures at 20 mW/cm 2 , colonic temperature remained constant while PO/AH temperature increased 0.2-0.3 8C because the T a selected was 2-3 8C cooler than normally preferred. Pilot experiments, in which an implanted tube was perfused with temperature controlled silicone oil to alter PO/AH temperature [Adair, 1988], indicated that autonomic thermoregulatory responses, for example, vasodilation, might play a mediating role in the mobilization of thermoregulatory behavior.…”

“…In contrast, when squirrel monkeys were exposed to 2450 MHz CW fields, thermoregulatory behavior efficiently regulated the skin and deep body temperatures at the normally preferred levels. This general finding includes partial body exposure [Adair, 1985], brief (10 min) exposures at SARs as high as 9 W/kg [Adair, 1987], and prolonged exposure (90-120 min) at SARs as high as 6 W/kg [Adair and Adams, 1983].…”

Human exposure at two radio frequencies (450 and 2450 MHz): Similarities and differences in physiological response

“…A third T dp sensor monitored chamber source air continuously. Sweating rate was calculated from the increase in T dp by using Antoine's equation and a modified gas equation [Wood, 1970;Adair, 1987] and stored for later analysis.…”